The present invention relates to a process for the treatment of an ore substantially comprising a calcium aluminophosphate, and it more specifically relates to treatment serving to extract therefrom phosphorus in the form of P.sub.2 O.sub.5.
It has long been known to treat natural phosphates with a strong acid, such as sulfuric acid, in order to solubilize the rock and recover the phosphoric acid from the leaching solution.
In general, the phosphatic rocks used are constituted by calcium phosphates, such as apatites containing a small quantity of other metals, such as aluminum or iron. However, there is another type of phosphatic rock able to supply phosphoric acid, namely, calcium aluminophosphate which is more particularly found in the Thies deposits in Senegal where aluminum extraction can be carried out in an advantageous manner. This ore is generally in the form of two phases having substantially identical compositions and represented by the standard formula: CaAl.sub.3 (PO.sub.4).sub.2 (OH).sub.5.H.sub.2 O. Numerous processes have already been proposed for the successful utilization of this ore and, more particularly, calcium aluminophosphates. Examples are thermal reductions supplying the phosphorus, alkaline leaching supplying an alkali metal phosphate, and an alkali metal aluminate which must then be separated to recover a phosphate and metallurgical alumina, wet acid leaching used with sulfuric acid supplying a calcium sulfate which is filtered, and a phosphoric ammonium sulfate solution which is precipitated in the form of alum by adding ammonium bisulfate, etc.
All these processes require numerous, complex, and time-consuming operations, which provide difficult separations of the aluminum and the phosphorus with low yields and often by-products, which it is difficult to utilize. For this reason, they are not used on an industrial scale. This is also the reason why the industry is seeking an industrially profitable process for leaching calcium aluminophosphate ores and for separating aluminum and phosphorus recoverable in a workable form.
It is, accordingly, an object of the present invention to provide an improved process for leaching calcium aluminophosphates.
It is a further object of the present invention to provide a process for treating calcium aluminophosphates, which process avoids the disadvantages of prior art processes described above.
It is also an object of the present invention to provide an improved process which is suitable for operations on an industrial scale.
Other objects will be apparent to those skilled in the art from the present description, taken in conjunction with the appended drawing, which is a flow diagram illustrating the embodiment of Example 3, below.